A string of senior Conservatives warned Theresa May’s Brexit strategy is risking the health of the economy in a parliamentary debate, during which the pound dropped to its lowest ever level against a basket of currencies.

Seven former ministers – including Claire Perry and Ken Clarke – were among MPs to raise concerns about the government’s approach, amid signals the prime minister could be heading towards a hard Brexit.

Perry voiced concern about the state of the pound. “I am extremely concerned about what has happened to sterling and interest rates since the prime minister’s comments at the party conference last week,” she said.

The PM's Brexit confusion is contagious | John Crace

Read more

The pound lost almost 1% of its value and reached its lowest ever level on a trade-weighted index against other currencies during a speech from Brexit secretary David Davis, before recovering slightly later in the day. Since the referendum on 23 June, the pound has lost nearly 18% of its value against the dollar.

Perry added: “The problem that [Davis] is not acknowledging is that many people in this country do not think that there is a policy to put the national interest first; they think that there is a policy to put people’s narrow ideological interests first. He should be setting out clearly how we will protect British jobs and businesses and putting ideology in the past, where it belongs.”

May has made it clear she intends to honour the result of the referendum vote and ensure controls on freedom of movement, but has not yet revealed how far she is prepared to give up access to the single market in order to achieve curbs on immigration.

At prime minister’s questions on Wednesday, she denied claims by Jeremy Corbyn, the Labour leader, that the government is presiding over a “shambolic Tory Brexit”.

But tensions ran high in parliament during the debate on the UK’s departure that followed, as several Conservative MPs said they were prepared to work with Labour in order to better hold the government to account over the type of Brexit it plans to pursue.

No 10 was so concerned that Tory MPs were prepared to vote in favour of Labour’s motion calling for proper scrutiny of Brexit that it promised a series of debates in the House of Commons before article 50 is triggered, while stopping short of promising a vote on the terms.

“The premise on which we are advancing is that we will have proper scrutiny. But it is not one where we will allow anyone to veto the decision of the British people,” said David Davis, the secretary of state for leaving the EU.

Daily Mail's attack on 'Bremoaners' reflects editor's Brexit fears

Read more

He said it was “not black or white” whether the UK would stay in the single market and he could go no further than talking about overarching aims because revealing the UK’s top priority would prove “extremely expensive”.

Those aims, he said, were: “Bringing back control of laws to parliament, bringing back control over decisions of immigration to the UK, maintaining the strong security cooperation that we have with the European Union, and establishing the freest possible market in goods and services with the European Union and the rest of the world.”

Davis also hit out at businesses and countries who were creating a “Brexit blame festival” which, he said, was making employees unnecessarily nervous about the consequences of leaving the EU.

Davis was supported by many of the most Eurosceptic MPs in parliament, including John Redwood, Bill Cash, Bernard Jenkin and Peter Bone. He and others have suggested that those calling for more parliamentary scrutiny are trying to “micromanage” the process or defeat the “will of the people”.

However, this argument was rebuffed by around a dozen of his Conservative colleagues who used the debate effectively to put May on notice that they will fight any attempt to push through a hard Brexit deal that they believe will harm the economy.

Meanwhile Clarke, a former chancellor, said no foreign companies would invest until there was more clarity about the UK’s future relationship with the outside world.

He said May’s conference speech potentially signalling an exit from the single market and customs union had caused a “reaction in the markets that was only too obvious”.

“It has continued ever since with continued pronunciations of uncertainty that are holding things back very badly. The pound has devalued to an extent that would have caused a political crisis 30 years ago when I first came here, and not for the first time.”

Chris Philp, a Tory backbencher, urged the Brexit secretary to give away more details, saying there was a “danger some [businesses] may take decisions in the next two or three months” to pre-emptively scale back investment and move jobs.

The debate was secured by Labour and opened by shadow Brexit secretary Keir Starmer, who said it was “frankly astonishing” that the government intended to avoid a vote on the terms on Brexit.

“I’ve stood here and accepted there’s a mandate for exit. There is no mandate for the terms. It has never been put to the country. It has not even been put to the secretary of state’s political party and it has not been put to this house. Where is the mandate on the terms?”

Dominic Grieve, a former attorney general, said there were likely to be economic risks and a “legal nightmare” caused by Brexit, as he argued there was a longstanding convention that major treaty changes must be approved by parliament rather than royal prerogative.

Nicky Morgan, the Conservative former education secretary, said she resented the implication from newspapers, ministers and “briefers and spinners at the heart of this government” that she was trying to block Brexit, and pledged to work even harder at holding the government to account over its role in leaving the EU.

She said she was “deeply concerned” that the cabinet had not been consulted on when article 50 would be triggered and spoke of her “heartbreak” that one of her constituents would find it difficult to carry on living in the UK as an EU citizen.

Anna Soubry, the former small business minister, said the country was facing difficult times and spoke of a small UK firm that was in danger of going under, and others that had told her EU workers were returning to their countries of origin.

“We should be holding our heads in shame that this is a feeling that people have,” she said.